Provided are an operating method of a host device, an operating method of a memory device, and a memory system. The operating method of a host device includes transmitting a request command for performing an eye-opening monitor (EOM) operation to a memory device, transmitting a parameter for performing the EOM operation to the memory device, transmitting pattern data for performing the EOM operation to the memory device, and receiving a first response signal including a result of the EOM operation performed based on the parameter and the pattern data from the memory device.